1. Field of the Invention
The present invention relates to a regulator protection circuit.
2. Description of the Prior Art
An example of the configuration of a conventional power supply apparatus is shown in FIG. 5. The power supply apparatus shown in FIG. 5 is composed of: an overvoltage detection circuit 11 that serves as a regulator protection circuit; and a regulator 10 that converts an input voltage VIN into a predetermined output voltage VOUT and then outputs it. When the input voltage VIN to the regulator 10 becomes equal to or higher than a detection level, the overvoltage detection circuit 11 turns the regulator 10 off; when the input voltage VIN to the regulator 10 becomes equal to or lower than the detection level (or, in a case where hysteresis is introduced, equal to or lower than a recovery level that is lower than the detection level), the overvoltage detection circuit 11 turns the regulator 10 on. In the power supply apparatus shown in FIG. 5, as a result of the overvoltage detection circuit 11 controlling the operation state of the regulator 10 in the manner described above, the regulator 10 is prevented from breakdown due to an overvoltage.
Another example of the configuration of a conventional power supply apparatus is shown in FIG. 6. In FIG. 6, such blocks an signals as are found also in FIG. 5 are identified with the same reference numerals and symbols. The power supply apparatus shown in FIG. 6 is composed of: a thermal shut-down circuit 12 that serves as a regulator protection circuit; and a regulator 10 that converts an input voltage VIN into a predetermined output voltage VOUT and then outputs it. The thermal shut-down circuit 12 is provided with a temperature sensing circuit (not illustrated). When the output voltage of the temperature sensing circuit becomes equal to or higher than a detection level, the thermal shut-down circuit 12 turns the regulator 10 off; when the output voltage of the temperature sensing circuit becomes equal to or lower than the detection level (or, in a case where hysteresis is introduced, equal to or lower than a recovery level that is lower than the detection level), the thermal shut-down circuit 12 turns the regulator 10 on. In the power supply apparatus shown in FIG. 6, as a result of the thermal shut-down circuit 12 controlling the operation state of the regulator 10 in the manner described above, the regulator 10 is prevented from breakdown due to overheat.
However, in the power supply apparatus shown in FIG. 5 described above, in response to successive overvoltage noise pulses, the overvoltage detection circuit 11 repeats detection of the overvoltage and recovery therefrom alternately, and thus the output of the regulator 10 repeats turning on and off alternately. This may cause malfunctioning of the load (for example, a microcomputer) to which the regulator 10 feeds its output.
On the other hand, in the power supply apparatus shown in FIG. 6 described above, when an overloaded state persists or in similar situations, the thermal shut-down circuit 12 detects overheat and turns the regulator 10 off. This temporarily lowers the temperature, but later, when the regulator 10 turns on, overheat occurs again. In this way, in the power supply apparatus shown in FIG. 6 described above, when an overloaded state persists or in similar situations, the thermal shut-down circuit 12 repeats detection of overheat and recovery therefrom alternately, and thus the output of the regulator 10 repeats turning on and off alternately. As a result, the regulator 10 is kept at temperatures around the overheat detection temperature for a long time. This degrades the reliability of the regulator 10.
In the wiper controlling apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-145022, when short-circuiting occurs a predetermined number of times in succession, the operation of the drive circuit is stopped. This helps prevent unnecessary repetition of overheat shut-down protection operation, and thus helps keep the reliability of the circuit satisfactorily high. However, in the wiper controlling apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-145022, also when it receives successive overvoltage noise pulses, it regards them as short-circuiting occurring a plurality of times, and thus stops the operation of the drive circuit. This may make the apparatus unusable simply in response to noise while in fact no short-circuiting is occurring.